The head shepherd was seen as a better matrimonial match than a driver

Following Ariejan Bos' comment, I think we can outline a possible solution. We assume Mr Walker's back story about an original Darracq engine fitted with Henriod valves has a solid origin. Grace's Guide to British Industrial History puts the introduction of the disastrous Darracq-Henriod engines to 1912. The commercial damage to the company started almost immediately, and apparently some cars even failed to leave the factory. We assume that one car did escape and was shipped to New Zealand, where its engine failed to last for very long before seizing. The owner was left with an expensive car, but, as luck would have it, there was a ca. 1908 Napier for sale cheaply. Even a 4-cylinder Napier was a big engine and we may be looking at a 6. Either way, the engine was fitted but the radiator had to sit out in front in a typical Napier way.

How can successful car designer's make such terrible mistakes? It reminds me of William Morris' 6 cylinder bullnose, a beautifully-proportioned car of which 50 were made. Unfortunately, Morris decided to economise on the engine and used standard bullnose parts (nothing wrong there), but with a 2-bearing, 6-journal crankshaft. These cars could barely be started without their crankshafts breaking. Morris realised his mistake and sadly decided not to stabilise the crankshaft with extra bearings. The remaining cars were buried under the Cowley factory.

I need to correct myself. The transition from square front edge to a more rounded form seems to have occurred about 1914, and may have coincided with the switch from acetylene lamps to CAV electric headlamps.

I doubt this is a Darracq. The immediate concern is the radiator, which clearly has a square front edge. That, together with its position well forward of the front axle, the tall radiator cap, and the long bonnet suggest it is a Napier. Darracq's from this period had round-edged radiators which sat slightly further back. However, I am not familiar with the hub-caps, which do not seem to be Napier.

If it is a Henriod-valved Darracq, its survival in functional order in 1915 would seem to be a minor miracle. The Henriod valve was a rotary valve that handled both inlet and exhaust, depending upon its rotational position. Darracq seems to have insisted that all engines after 1911 were fitted with the valve, but accounts suggest these engines were complete dogs. Darracq was forced out of the company bearing his name as a direct result, either in 1912 or 1913, and he appears to have sold out of the company at about the same time. A commercial rescue operation was mounted in which the engines were replaced by Rover engines. Apart from performance, the Henriod valve tended to seize. This is not surprising. A cross-sectional diagram in the Wikipedia article on Alexandre Darracq shows it to have a substantial area of contact with the cylinder it rotates in, and lubrication must have been a problem, particularly with the hot exhaust gases.

At first I had serious doubts if this car was a Darracq. Then I decided that most of the car is Darracq, except for the bonnet and radiator. The radiator is too wide and is placed well ahead of the front axle, which you never see with a Darracq. So the question for me is: what happened? Accident perhaps? Or improved cooling?